17.the Atmosphere-Structure and Temperature

7/31/2019 17.the Atmosphere-Structure and Temperature

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PrenticeHallEARTH SCIENCE

Tarbuck Lutgens


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Chapter

17The Atmosphere: Structure

and Temperature


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Composition of the Atmosphere

17.1 Atmosphere Characteristics

Weather is constantly changing, and itrefers to the state of the atmosphere at any

given time and place. Climate, however, isbased on observations of weather that havebeen collected over many years. Climatehelps describe a place or region.


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Major Components Air is a mixture of different gases and particles,

each with its own physical properties.


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Volume of Clean, Dry Air


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Variable Components

Water vapor is the source of all clouds and

precipitation. Like carbon dioxide, water vaporabsorbs heat given off by Earth. It also absorbssome solar energy.

Ozone is a form of oxygen that combines three

oxygen atoms into each molecule (O3). If ozone did not filter most UV radiation and all of

the suns UV rays reached the surface of Earth,

our planet would be uninhabitable for many

living organisms.


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Human Influence

Emissions from transportation vehicles account

for nearly half the primary pollutants by weight.


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Primary Pollutants


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Height and Structure of theAtmosphere


The atmosphere rapidly thins as you travel

away from Earth until there are too few gasmolecules to detect.

Atmospheric pressure is simply the weight of theair above.

Pressure Changes


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Atmospheric Pressure vs. Altitude


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Temperature Changes The atmosphere can be divided vertically into four

layers based on temperature.

The troposphere is the bottom layer of theatmosphere where temperature decreases with an

increase in altitude. The stratosphere is the layer of the atmosphere

where temperature remains constant to a heightof about 20 kilometers. It then begins a gradual

increase until the stratopause.


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Snowy Mountaintops Contrast withWarmer Snow-Free Lowlands


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Temperature Changes

The mesosphere is the layer of the atmosphereimmediately above the stratosphere and ischaracterized by decreasing temperatures withheight.

The thermosphere is the region of theatmosphere immediately above the mesosphereand is characterized by increasing temperaturesdue to the absorption of very short-wave solarenergy by oxygen.


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Thermal Structure of the Atmosphere


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Earth-Sun Relationships


Earths Motions Earth has two principal motionsrotation and

revolution.Earths Orientation Seasonal changes occur because Earths

position relative to the sun continually changes

as it travels along its orbit.


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Tilt of Earths Axis


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Solstices and Equinoxes The summer solstice is the solstice that occurs

on June 21 or 22 in the Northern Hemisphereand is the official first day of summer.

The winter solstice is the solstice that occurs onDecember 21 or 22 in the Northern Hemisphere

and is the official first day of winter.


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Solstices and Equinoxes The autumnal equinox is the equinox that

occurs on September 22 or 23 in the NorthernHemisphere.

The spring equinox is the equinox that occurson March 21 or 22 in the Northern Hemisphere.


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Length of Daylight


The length of daylight compared to thelength of darkness also is determined by

Earths position in orbit.


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Solstices and Equinoxes


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Energy Transfer as Heat

17.2 Heating the Atmosphere

Heat is the energy transferred from oneobject to another because of a difference in

the objects temperature.Temperature is a measure of the averagekinetic energy of the individual atoms ormolecules in a substance.


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Three mechanisms of energy transfer asheat are conduction, convection, and

radiation.

Conduction is the transfer of heat throughmatter by molecular activity.

Conduction

Convection is the transfer of heat by massmovement or circulation within a substance.

Convection


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Electromagnetic Waves The sun emits light and heat as well as the

ultraviolet rays that cause a suntan. These formsof energy are only part of a large array of energyemitted by the sun, called the electromagneticspectrum.


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Electromagnetic Spectrum

Vi ibl Li ht C i t


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Visible Light Consistsof an Array of Colors


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Radiation Radiation is the transfer of energy (heat)

through space by electromagnetic waves thattravel out in all directions.

Unlike conduction and convection, which need

material to travel through, radiant energy can

travel through the vacuum of space.


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Radiation All objects, at any temperature, emit radiant

energy. Hotter objects radiate more total energy per unit

area than colder objects do.

The hottest radiating bodies produce the shortest

wavelengths of maximum radiation. Objects that are good absorbers of radiation are

good emitters as well.


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What Happens to Solar Radiation?


When radiation strikes an object, thereusually are three different results.

1. Some energy is absorbed by the object.

2. Substances such as water and air aretransparent to certain wavelengths of radiation.

3. Some radiation may bounce off the object

without being absorbed or transmitted.


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Solar Radiation


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Reflection and Scattering Reflection occurs when light bounces off an

object. Reflection radiation has the sameintensity as incident radiation.

Scattering produces a larger number of weakerrays that travel in different directions.


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Absorption

About 50 percent of the solar energy that strikes

the top of the atmosphere reaches Earthssurface and is absorbed.

The greenhouse effectis the heating of Earthssurface and atmosphere from solar radiation

being absorbed and emitted by the atmosphere,mainly by water vapor and carbon dioxide.


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Why Temperatures Vary

17.3 Temperature Controls

Factors other than latitude that exert astrong influence on temperature include

heating of land and water, altitude,geographic position, cloud cover, andocean currents.


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Land and Water Land heats more rapidly and to higher

temperatures than water. Land also cools morerapidly and to lower temperatures than water.

Mean Monthly Temperatures


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Mean Monthly Temperaturesfor Vancouver and Winnipeg


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Geographic Position The geographic setting can greatly influence

temperatures experienced at a specific location.

Mean Monthly Temperatures for


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Mean Monthly Temperatures forEureka and New York City

Mean Monthly Temperatures


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Mean Monthly Temperaturesfor Seattle and Spokane


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Altitude The altitude can greatly influence temperatures

experienced at a specific location.

Mean Monthly Temperatures for


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Mean Monthly Temperatures forGuayaquil and Quito


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Cloud Cover and Albedo

Albedo is the fraction of total radiation that is

reflected by any surface. Many clouds have a high albedo and therefore

reflect back to space a significant portion of thesunlight that strikes them.


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Clouds Reflect and Absorb Radiation


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World Distribution of Temperature


Isotherms are lines on a weather map thatconnect points where the temperature is

the same. Isotherms generally trend east and west and

show a decrease in temperatures from thetropics toward the poles.

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17.the Atmosphere-Structure and Temperature